At the beginning of the 1970s, the presence of T lymphocytes capable of suppressing immune responses was described for the first time. At that time, it was believed that said suppressive action was mediated by a specific cell subpopulation, but no specific marker of said subpopulation was managed to be cloned or characterized and the interest for this cell subtype was partly lost. However, in 1995, Sakaguchi et. al. (Sakaguchi et al. 1995. J Immunol 155:1151-64) discovered that a minority population of CD4+ cells (10%) which co-expressed the interleukin 2 receptor alpha chain (CD25) was crucial for controlling autoreactive cells and autoimmunity in vivo. Since then, many groups have demonstrated that this subpopulation of CD4+CD25+ cells, also known as Treg lymphocytes or Treg cells, are immunosuppressive (Takahashi et al. 1998. Int Immunol 10:1969-80; Thornton & Shevach. 1998. J Exp Med 188:287-96). These cells were first identified in mice but have later been extensively characterized in humans (Dieckmann et al. 2001. J Exp Med 193:1303-10; Jonuleit et al. 2001. J Exp Med 193:1285-94; Levings et al. 2001. J Exp Med 193:1295-302). The existence of a specific immunosuppressive subpopulation is currently widely accepted by the scientific community and the way to manipulate its activity for its clinical use is sought. The main issue is how its activity could be modulated.
Treg lymphocytes are essential for the protection against autoimmune diseases and for the prevention of rejection to transplants; therefore, the posibility of enhancing their activity has a great potential in the treatment of the autoimmune diseases and in organ transplants. However, due to the fact that tumors express autoantigens, Treg lymphocytes can be capable of inhibiting the activation of immune responses against cancer.
Several groups, including the group of the inventors, have demonstrated that the simple elimination of CD4+CD25+ (Treg) cells by the in vivo administration depleting antibodies facilitates the induction of antitumor immunity and the protection against cancer development (Casares et al. 2003. J Immunol 171:5931-9; Onizuka et al. 1999. Cancer Res 59:3128-33; Shimizu et al. 1999. J Immunol 163:5211-8; Steitz et al. 2001. Cancer Res 61:8643-6; Sutmuller et al. 2001. J Exp Med 194:823-32). It is thus believed that CD4+CD25+ (Treg) cells are continuously slowing down the activation of effector T lymphocytes to prevent autoimmunity processes, but at the same time making the correct activation of an antitumor response difficult when it is necessary.
Immunotherapy is very promising for the treatment of patients with cancer. The numerous clinical protocols carried out which have used therapies based on cytokines, infusions of effector T cells or vaccination protocols have demonstrated that cancer immunotherapy is generally safe. However, although the induction of immune responses after the treatments has been observed in these clinical protocols, most of the patients are incapable of developing an effective antitumor response. A meta-analysis of 37 independent clinical vaccination protocols including more than 700 patients has showed that the percentage of partial or complete responses against the tumor is very low (3.8%) (Rosenberg et al. 2004. Nat Med 10:909-15). The recent demonstration of the presence of Treg lymphocytes in the tumor tissue or the lymph nodes of patients with melanoma (Wang, H. Y., J Immunol, 2005. 174:2661-2670; Viguier, M., F. J Immunol, 2004. 173:1444-1453), lung cancer (Woo, E. Y., Cancer Res 61:4766-4772), ovarian cancer (Woo, E. Y., Cancer Res, 2001. 61:4766-4772, Curiel, T. J., Nat Med, 2004. 10:942-949), pancreatic cancer and breast cancer (Liyanage, U. K., J Immunol, 2002. 169:2756-2761) as well as in hepatocarcinomas (Ormandy, L. A. Cancer Res, 2005. 65:2457-2464; Kobayashi, N., Clin Cancer Res, 2007. 13:902-911) and the description that tumor tissue secretes chemokines which specifically attract this subpopulation towards tumor tissue indicate that the access of Treg lymphocytes to the tumor is a dynamic process and that it exerts an immunosuppressive effect facilitating the progression of the disease. The presence of Treg in the tumor as well as in peripheral nodes could explain the low efficacy of the immunotherapy protocols. In the same way, in infectious diseases, the control exerted by Treg lymphocytes can limit the magnitude of the effector T responses and cause the failure in the control of the infection. It has thus been described that some viruses such as hepatitis B virus (Xu, D. J Immunol, 2006. 177:739-747), hepatitis C virus (Boettler, T., J Virol, 2005. 79:7860-7867; Cabrera, R. Hepatology, 2004. 40:1062-1071; Rushbrook, J Virol, 2005. 79:7852-7859; Sugimoto, K. Hepatology, 2003. 38:1437-1448) and HIV, (Aandahl, E. M. J Virol, 2004. 78:2454-2459; Kinter, A. L. J Exp Med, 2004. 200:331-343; Oswald-Richter, K. PLoS Biol 2004. 2:E198; Weiss, L. Blood, 2004. 104:3249-3256) can use Treg lymphocytes to block the antiviral immune response and thus allow the establishment of the persistent chronic infection. Due to all this, it is believed that the modulation of the action of Treg lymphocytes can be essential in the development of immunotherapies against cancer or against infectious diseases.
There is a certain controversy with regard the mode of action of Treg lymphocytes, but the role of cytokine TGF-β (transforming growth factor-β) in the process for inhibiting effector T cells seems to be increasingly coherent (Powrie et al. 1996. J Exp Med 183:2669-74; Somasundaram et al. 2002. Cancer Res 62:5267-72).
In addition, it has recently been described that the transcription factor scurfin (FOXP3, expression product of the foxp3 gene) (Yagi et al. 2004. Int Immunol 16:1643-56. 2004 Oct. 4) is essential for the activity of Treg lymphocytes, such that its presence determines the suppressive activity of these cells. The cDNA sequences encoding murine and human scurfin have been the object of U.S. Pat. No. 6,414,129 which furthermore describes that the modulation of the expression of scurfin can have therapeutic effects in various diseases; said patent also mentions the use of synthetic peptides, among other molecules, to regulate the expression of the foxp3 gene but does not mention anything about the possibility of inhibiting the activity of the already expressed scurfin.
Likewise, the use of a method for enhancing the immune response in mammals based on the elimination of Treg lymphocytes by means of using neutralizing monoclonal antibodies (WO 2006/044864); however, said patent application does not mention anything about the transient regulation of the activity of Treg lymphocytes by means of inhibiting the activity of scurfin (essential in the immunosuppressive effect of said cells). In addition, the depletion of Treg lymphocytes increases the risk of induction of autoimmunity and the fact that such monoclonal antibodies do not discriminate between Treg lymphocytes and effector T lymphocytes reduces their application.
Currently, the only methods for inhibiting the activity of Treg lymphocytes which have been experimentally described involve their elimination, by means of using depleting antibodies or by means of blocking the cytokines that they produce and which may be responsible for their activities (TGF-β, IL-10), but there is no specific inhibitor of this cell subpopulation. The methods which are based on the depletion of the regulatory T cells have the drawback that they eliminate the cells and involve risks of causing autoimmune diseases. Furthermore, there are no specific antibodies for regulatory T cells and those that exist can also eliminate effector T cells.
It is therefore still necessary to identify new compounds capable of regulating or blocking the activity of Treg lymphocytes, potentially useful in human therapy.